This invention relates to face masks, and more particularly to face masks wherein the filter consists of a repulsive filtering media.
Face masks are well known in the prior art, especially for industrial and medical purposes. Early face masks were made from cloth, such as gauze or linen, and usually consisted of a plurality of layers (see U.S. Pat. No. 1,292,095). While these masks had good air permeability, they had poor filtration ability. As such, they were suitable for filtering large dust particles, but were poor at filtering small particles, e.g. pollen and microbes. The layers of cloth would entrap various particulate matter, and even though the cloth might have been washable, washing would not remove all of the particles. The constant necessity for washing also caused wear and deterioration of the filtering medium. These cloth type filter mediums were also poor at maintaining a specific filtering accuracy.
Non-woven, melt blown or molded filters of a mat matrix (e.g. U.S. Pat. No. 3,220,409) provide a filtering medium that is suitable for filtering smaller particles than cloth type filters. Like cloth filters, these mat filters entrain particulates on or within the matrix medium. They are also absorbent and cannot be washed or cleaned because the filtering medium would fall apart. These filters have a very limited life and are known as "disposables". In order to achieve a greater filtering ability, the mat matrix mediums of these filters have a built up thickness and an indirect air flow through the medium so that they have a reduced air permeability and require a stronger breathing effort.
There exists a need for a face mask with a filter medium having a high degree of filtration, a high air permeability capacity, that does not clog or entrain particulate matter, that has a long life, and that has a wide range of applications.